1. Field of the Invention
The invention relates to a key switch device and, more particularly, to a key switch device suitably used in a thin keyboard associated with a notebook-size word processor, notebook-size personal computer, etc.
2. Description of the Related Art
In general, a conventional key switch device has a structure such that a circuit board in the form of an insulated film is sandwiched between a holder member and a switch supporting plate as described in Japanese Patent Application No. Hei 3-330160 (corresponding to U.S. Pat. Nos. 5,280,147 and 5,278,372.
On the film circuit board are printed two kinds of switching circuits and a plurality of fixed contact patterns each consisting of two fixed contacts extending from the two kinds of switching circuits and combined in a comb-shaped manner. An inverted cup-shaped rubber spring is located at a position corresponding to each fixed contact pattern. A movable contact is provided in the rubber spring and, when the rubber spring is depressed, a switching operation is effected.
An actuator is provided in the holder member over the rubber spring, and a key top is mounted on the upper end of the actuator. When the key top is depressed by an operator, it is guided by the actuator to the upper portion of the rubber spring, and the rubber spring is depressed by the actuator. When an amount of depression of the rubber spring exceeds a certain limit, the movable contact in the rubber spring comes into contact with the fixed contact pattern, thereby short-circuiting the two fixed contacts and effecting the switching operation.
The switch supporting plate corresponds to a lower cover of a keyboard device and serves to enhance the rigidity of the keyboard device and improve the reliability of key entry.
Recent word processors, personal computers, etc. have been reduced in size, especially in thickness, weight, and cost. In association with this trend, a keyboard associated with such equipment is required to be reduced in size, thickness, and weight.
On the other hand, a movable portion of any key of the keyboard is required to have a good operability in view of human engineering (it is generally known that a minimum key stroke of 3 to 4 mm is required for an operator to recognize depression of the key). Accordingly, the above requirement must be satisfied with the minimum key stroke maintained.
In most cases, however, peripheral parts of the actuator and the holder member are formed mainly of a resin material by injection molding. Accordingly, a minimum wall thickness of 1.5 mm in each member is necessary. This connotes that the greater the number of parts to be laminated, the more difficult the reduction in thickness and, of course, the higher the weight.
Further, the conventional key switch device has three-layer structure consisting of the holder member, the film circuit board, and the switch supporting plate. Unless these three layers are laminated uniformly and closely, the reliability of response to key entry is deteriorated. As countermeasures against such a problem, it is known to suppress separation of these three layers at every key or at given intervals. However, much trouble is taken to ensure the suppression.
It is accordingly an object of the invention to provide a key switch device having an integrated structure of a substrate, an electrical circuit pattern, and a mounting portion for mounting a guide supporting member, which can reduce the number of parts, simplify the construction, reduce the size, especially the thickness of the keyboard, ensure a sufficient key stroke, and obtain good key operability and reliable key entry.